On the amino acids in the urine of dairy cows fed urea as the sole or partial source of nitrogen
Abstract
The urinary amino acids in free and bound form were determined quantitatively in dairy cows fed urea and ammonium nitrogen as the sole (0-cows) or partial (ULP-cows) source of nitrogen. For comparison, amino acid determinations were performed also on the urine of cows on ordinary silage-cereals feed and pasture feed (NorP-cows). The total amount (mg/1 urine) of the free amino acids was the smallest with 0-cows and the highest with NorP-cows on pasture feeding. The difference was mainly due to glycine ,which was found in significantly higher (P < 0.001) amounts with NorP-cows on pasture feeding. The proportion of glycine in the total identified free amino acids was 9.7 ± 9.0 % with 0-cows, 13.5 ± 5.1 % with ULP-cows, 7.7 ±3.4 % with NorP-cows on indoor feeding and 56.4 ±21.0 % with NorP-cows on pasture feeding. The corresponding figures for glutamic acid, which was quantitatively the most important amino acid with 0- and ULP-cows, were 36.5 ± 29.6 %, 19.8 ± 19.2 %, 5.7 ±4.0 % and 3.9 ± 2.1 % of the total free amino acids. Besides the identified amino acids, there were a number of unidentified amino acid derivatives in the free amino acid fraction in all the feeding groups. The total amount of amino acids freed by hydrolysis was the lowest with 0-cows. The proportion of glycine of the amino acids of the hydrolysate was48 % with 0-cows, 66 % with ULP-cows and 84 % with NorP-cows.Downloads
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